This application is a 371 of PCT/EP00/09016 filed Sep. 15, 2000.
The invention relates to an application device for a vehicle brake, particularly for a rail vehicle brake.
An application device of the above-mentioned type is known from Patent Document 195 14 463 C.
This document describes a combination of a pneumatic service brake and a spring-loaded parking brake. The spring-type accumulator is inserted by a complete bleeding of the spring accumulator cylinder.
European Patent Document EP 0 125 873 B1 describes a brake actuator having an electric-motor drive for tensioning a spring-type accumulator. In the case of the spring accumulator service brake, the maximal application force can be adjusted by a displaceable elastic stop.
Furthermore, European Patent Document EP 0 693 633 A2, a permanent-magnet brake shows that the application force is generated by two magnet arrangements. The two magnetic forces can be mutually added or subtracted.
Furthermore, U.S. Patent Document U.S. Pat. No. 5,620,077 describes a spring-type accumulator service brake in the case of which an electric motor is used for tensioning a spring-type accumulator. The electric motor and the spring-type accumulator, as the brake actuator, are connected with one another by an electrically operable coupling device. The brake actuator with the spring-type accumulator operates such that the release position is reached by compressing the spring. However, the spindle operates in only one direction, specifically the direction of the tensioning of the spring. As a result of a design which is such that the brake is spring-actuated and that electric energy is required for releasing the brake or for compressing the spring, a xe2x80x9cfail-safe designxe2x80x9d of the brake is achieved.
Essentially two wheel brake systems are currently used in the rail vehicle field: Pneumatic brake systems (which may include electropneumatic systems and vacuum brakes) and (electro)hydraulic brake systems. Purely electromechanical brake systems have been unable to establish themselves to any significant extent in the market.
In both technologies, the force is generated by pistons in cylinders which generally have only one operating direction. The restoring of the pistons takes place as a result of the forces occurring because of the elastic deformation of the brake linkage as well as a result of restoring springs which, in addition, ensure the taking-up of an end position. Special constructions having a double cylinder (that is, with a possible pressure buildup at each side of the piston for implementing two operating directions) have not been successful, particularly for cost reasons.
Also because of the preferred use of pistons with only one operating direction, when a brake system is configured, either an active or a passive brake system is implemented. However, these systems require high-powered drives or, in the case of electromechanical systems, correspondingly large engines. In addition, in the case of a passive system, a very large adjusting spring is required.
The local energy storage in the event of supply interruptions in the case of pneumatic systems takes place in compressed-air reservoirs; in the case of hydraulic systems, it takes place in corresponding hydraulic reservoirs; and in the case of electromechanical systems, by booster batteries or a redundant power supply. In addition, passive systems contain the possibility of a one-time application as a result of the energy accumulated in the spring.
In the case of an active brake system, the maximal actuator force must be applied during a braking at a maximal braking force, whereas, in the case of a passive brake system, the full actuator force is used for the release.
A disk brake of the above-mentioned type for motor vehicles is also known from U.S. Patent Document U.S. Pat. No. 4,784,244.
In view of this background, the invention has the object of providing an application device whose braking force generator or brake drive and parts of its braking force converter can have significantly smaller dimensions when compared to the actively operating brake system as well as to the passively operating brake system.
The invention achieves this as follows:
At a defined operating point or for a brake application force value between zero and the maximal braking force, the brake drive or the braking force generator has no effect. At this point, the braking force is generated only by the energy accumulator (for example, the spring). This xe2x80x9czero pointxe2x80x9d of a pure generating of spring braking force is also not at the maximal braking force as in the case of the purely passive system. On the contrary, for generating the maximal braking force, the braking force (and energy) generator or the brake drive is additionally operative. For generating lower braking forces, the brake drive acts virtually as a xe2x80x9cbaking force reducerxe2x80x9d against the force of the energy accumulator or the spring force.
In contrast to the prior art, the brake drive is therefore used in both load directions, that is, for applying the maximal braking force as well as for releasing the brake. As a result, a converter is designed such that, also when the brake drive is switched off, for example, a medium braking force is applied. Only a type of xe2x80x9csupporting drivexe2x80x9d is required in order to adjust either the maximal braking force or the braking release position. The brake drivexe2x80x94in the case of an electromechanical system, an electric motor-is utilized for reducing the spring force during the release and, during then braking, after the force equilibrium between the brake application force and the spring force has been reached, further increasing the braking force. The drive therefore operates in the manner of a xe2x80x9ctwo-direction principlexe2x80x9d. Thus, the system combines important advantages of a passive brake system with advantages of an active brake system. Similar to a passive brake system, the system according to the invention with the zero-point displacement also implements a type of fail safe system. An accumulator spring for the brake application can be implemented to be considerably smaller than in the case of a purely passive brake system. In the case of an electric drive, the spring as well as its tensioning and driving motor can be dimensioned to be up to one half smaller because of the invention. In which case, however, the advantage may be arbitrarily and continuously reduced by increasing load accumulations, the definition of certain residual braking forces in the event of a failing of the brake, the parking brake, and a soft spring characteristic.
Since, in contrast to an active brake system, the brake drive does not have to generate the braking force by itself, the brake drive, as well as the entire transmission line, can have a smaller dimension than in the case of a purely active system.
Another advantage of the invention is that control operations within the range of the medium braking force by means of the invention require only low adjusting energies.
The converter is designed to adjust the force applied by the brake drive in ranges about an operational zero point. The range may be between 25 and 75%, or between 40 and 60% or at 50%. Often, for example, in the event of a failure of electric energy, a braking force of 50% of the maximal braking force will be sufficient as a safe fall-back level. The operational zero point can essentially be freely selected. In this case, the person skilled in the art can orient himself according to the respective safety requirementsxe2x80x94specifically vehicle and route parametersxe2x80x94of the application case. Thus, he will, for example, place the zero point for the implementation of sufficient braking reserves when designing a street car braking system for a city with many down grades several percent xe2x80x9chigherxe2x80x9d than in a city whose street car system is largely free of extensive down grades.
Particularly preferably, an electric motor is used as the brake drive, which can have a highly compact design as a result of the invention. However, as an alternative, it is also conceivable that the brake drive is a hydraulic or pneumatic brake cylinder (operating in two directions) or another unit operating in one or two directions.
In each case, a spring or a spring assembly is a suitable energy accumulator. The spring or the spring assembly is preferably designed such and coordinated with the converter and the brake drive that, by means of it, when the brake drive is not active, a defined, particularly a medium braking force can be generated. In particular, the electric motor and the spring or the spring assembly are mutually coordinated such that
the spring or the spring assembly alone generates a defined braking force value between the minimal and the maximal braking force (operational zero point),
the spring and the electric motor, in an addition of forces, generate a braking force greater than the defined braking force at the operational zero point, and
the spring and the electric motor, in a subtraction of forces, generate a braking force less than the operational zero point. As a result of this embodiment of the invention, the electric motor as well as the spring or the spring assembly can have a smaller design than in the case of a purely active or passive electromechanical braking system in which the spring or the electric motor alone must in each case generate the maximal braking or releasing force.
Additional advantageous embodiments of the invention are described.